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Background: Know: Recognize: Prerequisites - Internet, multiplexing, gateways, hosts Internet design goals Goals Importance Order Description Goals Level Interconnection 1 As we all know, the Internet consists of various networks. To provide larger and better service, these separate networks are to be interconnected firstly. Based on this, interconnection is the fundamental goal for the design of the Internet architecture. In addtion, circuit switching, packet switching etc. are examples of techniques used to interconnect networks effectively. Top level Failure recovery 2 Various security vulnerabilities happen at every level now, for example, eavesdropping, prefix hijacking, IP spoofing, SYN floods etc, which can result in the failure of Internet communications. Therefore, the Internet architecture must be able to continue to provide communication services despite of the failure. Second level Multiple types of service 3 With the development of Internet techniques, the Internet gives a new birth to many communication services. For example, online shopping, Internet forums, instant messaging, IPTV etc. These new types of service help greatly improve the forms of human interactions. And the third most important goal is to support such multiple types of service. Second level Variety of networks 4 In modern society, a wide number of people can use communication networks to exchang and transmit information through a system of symbols, writing, signals or speech. Local Area Network(WLN), Wireless Network, Wide Area Network(WAN) are some examples of these communication networks. In the respect of robustness, the Internet architecture must support a variety of networks. Second level Distributed Management of resources 5 As the use of Internet has grown, a large number of Internet resources are to be managed. This goal means that the Internet resources are not managed only by the same agency. Actually, there are various management agencies, and each manages a set of resources. For example, the distributed management of routers and gateways. Second level Cost-effective 6 The Internet architecture must be cost effective. Second level Low entry-cost 7 The Internet architecture must permit host attachment with a low level of effort. Second level Accountability for resources 8 This goal is the least important and it can be achieved by monitoring the usage of the Internet resources. Second level The goals mean the reasoning and motivation that leads to the design of Internet architecture. Different levels of goals are discussed in 'The design philosophy of the DARPA Internet protocols' . Table 1: Different levels of goals. Note that the goals in this table are listed in order of importance. A value 1 means most important, while a value 8 means least important. In addition, the last three goals are less important than other second level goals. The paper gives an example of how the decision to use datagrams (which facilitates the goals of interconnection of existing networks and of continued operation despite loss of networks or gateways) makes it harder to manage the network: "While the datagram has served very well in solving the most important goals of the Internet, it has not served so well when we attempt to address some of the goals which were further down the priority list. For example, the goals of resource management and accountability have proved difficult to achieve in the context of datagrams. As the previous section discussed, most datagrams are a part of some sequence of packets from source to destination, rather than isolated units at the application level. However, the gateway cannot directly see the existence of this sequence, because it is forced to deal with each packet in isolation. Therefore, resource management decisions or accounting must be done on each packet separately. Imposing the datagram model on the internet layer has deprived that layer of an important source of information which it could use in achieving these goals." References D. Clark: “The Design Philosophy of the DARPA Internet Protocols”, Proc. SIGCOMM, pp. 106-114, 1988. Different types of communication networks: http://www.ehow.com/list_7620661_different-types-communication-networks.html. Category:All